~
The fact that there is no Yamal is not the reason for the defeat and draw in the last two matches by Barcelona. Revisit the matches and you will see that they had mistakes elsewhere, moreover Yamal is not Barcelona's most prolific scorer, he is an important player in the squad but not the main one. Real are actually on Barcelona's heels, even with their game in hand it's really hard to predict what the outcome will be at the end of the season.
But I think it can be said that Yamal has a lot to contribute to the game and besides Raphinha is the most successful in giving assists to his mates. It is astonishing how this little kid is able to read the game and how to find the right spots with his incredibly precise long range passes. That's really impressive and I can't recall whether I have seen a 17 years old boy playing like that. It sometimes looks as if he lacks some speed, but I don't know.
I agree with you that Barcelona can't blame draws on losses on Yamal missing the game because of injuries. He is an important player as you put it, but he should not be the reason why they lose as soon as he is not able to play. That would overemphasize his importance.
They have several amazing scorers and the games were full of mistakes and not very well played. That was the reason why the left points on the table.